The perhaps not-so-secret nature of California’s major reservoirs — the big artificial lakes designed to impound floodwaters and snowmelt coursing down the state’s biggest rivers — is that they’re little more than big bathtubs. We depend on a beneficent nature to turn on the taps every winter and fill them. And we pull the plug every spring to drain them for use by farms and cities far away. Drought, not very beneficent to us or to anything else that might depend on water, interrupts the cycle of filling and emptying.